Cables which transmit information from one point to another by lo use of light energy and which utilize glass, plastic, or other signal carriers are typically referred to as fiber optic cables or optical data transmission cables. Fiber optic cables include optical fibers that typically are fabricated by drawing down a glass rod that contains a core region and a cladding region. The resulting drawn fibers provide a transmission path in the core region for light energy. When compared to metallic wire cables, fiber optic cables are superior in several respects.
For example, fiber optic cables have more possible signal channels because they utilize a wider band width than the electromagnetic band width used with metal conductors. Additionally, fiber optic cables typically have lower dB losses, and therefore have a much greater efficiency than metallic conductor systems.
However, metallic conductor systems have one great advantage over fiber optic systems in that metallic conductors are much stronger than fiber optic cables since most fiber optic cables are made of glass. If a fiber optic cable is subject to vibrations, severe bending, flexing, twisting or any other mechanical or physical force, the fiber may break, whereas in a system utilizing metallic conductors, the chances of breakage are much less. Additionally, when a fiber optic cable is bent, some of the energy may pass through the fiber cladding and be absorbed by the fiber coating. This may create a localized loss of light which is indicated by a reduction in the transmitted power. Different fiber and cable constructions have been found to provide various magnitudes of loss for a given fiber bend.
One example of when bending and possible breakage of fiber optic cables may occur is in a system having a bundle or harness containing a plurality of fiber optic cables. Along the length of the fiber optic cable harness, break-outs are provided wherein one or more of the fiber optic cables in the harness branch out for connection to a particular component within the system.
A fiber optic cable harness typically consists of multiple cable (termini-to-termini) segments secured in a bundle. The fiber optic cable harness is usually constructed by tying a bundle of fiber optic cables (segments) with spot ties (cable ties) made of a material such as MIL-T-43435 type II polyester lacing tape. In a harness having more than two connectors, groups of fiber optic cables are routed to each connector in break-outs from the main harness (trunk line) in a "T" pattern. Cable ties are used to hold the bundled cable segments together and to form the break-outs. The break-outs are formed by tying the trunk line on either side of the break-out location and bending the applicable segments away from the trunk line to form a branch. The branch is then secured into a bundle with additional cable ties.
During formation of a harness, a sharp bend may occur in individual cable segments at the break-out locations. This may occur due to excess tension being applied to one or more of the cables within the break-out bundle when an installer pulls on the branch. Excessive dB losses may occur at the location of a sharp bend. If the bend in a branch is excessive and the tension on the branch is large, individual fiber optic cables may crack or otherwise sever, resulting in a total loss of signal transmission.